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Date:   Mon, 9 Nov 2020 07:03:26 -0800
From:   Keith Busch <kbusch@kernel.org>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-mm@kvack.org, iommu@lists.linux-foundation.org,
        Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Ira Weiny <iweiny@intel.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: Re: [RFC PATCH 15/15] nvme-pci: Allow mmaping the CMB in userspace
Message-ID: <20201109150326.GA2221592@dhcp-10-100-145-180.wdc.com>
References: <20201106170036.18713-1-logang@deltatee.com>
 <20201106170036.18713-16-logang@deltatee.com>
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On Fri, Nov 06, 2020 at 10:00:36AM -0700, Logan Gunthorpe wrote:
> Allow userspace to obtain CMB memory by mmaping the controller's
> char device. The mmap call allocates and returns a hunk of CMB memory,
> (the offset is ignored) so userspace does not have control over the
> address within the CMB.
> 
> A VMA allocated in this way will only be usable by drivers that set
> FOLL_PCI_P2PDMA when calling GUP. And inter-device support will be
> checked the first time the pages are mapped for DMA.
> 
> Currently this is only supported by O_DIRECT to an PCI NVMe device
> or through the NVMe passthrough IOCTL.

Rather than make this be specific to nvme, could pci p2pdma create an
mmap'able file for any resource registered with it?